This application claims the priority of German Patent Document DE 100 54 007.4, filed Nov. 1, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a motor vehicle with a drive combustion engine and a power supply system.
The electric power, available for the electric consuming devices on-board a motor vehicle, is based in particular on the size and capacity of the electric generator, which usually exhibits a power output ranging from 1.5 to 2.5 kW. Thus, some electric consuming devices can be operated only when the internal combustion engine is on.
DE 197 03 171 A1 discloses a motor vehicle that is driven by a drive combustion engine and which contains a fuel cell system as the current generator (APU auxiliary power unit). This system supplies the electric consuming devices in the motor vehicle with energy and can be activated independently of running the internal combustion engine. The fuel cell system also supplies the drive combustion engine with electric energy. A battery is connected to the fuel cell system to release current as soon as the combustion engine is started and covers brief peak loads. Thus, the fuel cell system, comprising fuel cells and gas generating system, and the battery form a hybrid system to supply electric energy.
An object of the present invention is to improve a motor vehicle of the generally known type such that an economical, compact and efficient integration of a hybrid system comprising fuel cells-APU and battery can be achieved.
This object has been by way of a motor vehicle in which the energy and/or material currents of the engine and fuel cell system are coupled together. The terms xe2x80x9cAPUxe2x80x9d and fuel cell system are used synonymously in the following description.
In particular, the following advantages are now obtainable with the present invention:
improved efficiency;
fuel savings;
use of common modules is possible;
lower overall height;
cost reduction;
reduced the start time of the gas generating system in the fuel cell system and the exhaust gas catalyst in the exhaust gas stream of the combustion engine;
reduction in emissions, in particular the starting emission.
In an advantageous currently contemplated embodiment of the present invention, the drive combustion engine and the fuel cell system are disposed in a common cooling circuit. The result is a compact configuration because there is no need for separate cooling systems for the internal combustion engine and the fuel cell system. If necessary, the cooler that is used can be enlarged compared to the conventional cooler for a motor vehicle.
The lines to transport the coolant in the cooling system are coupled advantageously from a thermal view point to the body of the motor vehicle. The lines can run inside or outside the body, for example, in the area of the door sill. The line length between the APU (for example, placed in the rear of the motor vehicle) and the cooler (for example, placed in the front of the motor vehicle) can be used advantageously as the cooling distance. The lines can be disposed, in particular, in continuous cavities through the body of the motor vehicle, thus economizing on cost intensive fastening material on the bottom side of the motor vehicle. The APU and internal combustion engine can resort to peak cooling capacities at different operating points because the engine needs the peak cooling capacity in drive mode and the APU needs it when the vehicle is standing still.
When air conditioning the interior of the motor vehicle in standing mode, the APU can be started, with the drive combustion engine off, to generate electric energy to cool the passenger interior. At low outside temperatures, the motor vehicle can be preheated by starting the gas generating system of the APU. To this end, it is unnecessary to start up the entire fuel cell system. The requisite electric energy can be taken from the battery. Thermal energy can be obtained by burning fuel.
In another advantageous configuration of the present invention, the gas generating system of the fuel cell system is coupled thermally with the exhaust gas line of the drive combustion engine. Thus, should the APU not be used when the drive combustion engine is running, the APU can be held at the appropriate operating temperature by dissipated engine heat. Thus, if necessary, the APU can be started significantly faster. On the other hand, in the start phase of the motor vehicle the APU can preheat the exhaust gas catalyst of the engine, thus reducing the exhaust gas emission at startup because the starting temperature of the catalyst is reached faster. It is also contemplated, however that the APU will preheat the drive combustion engine by way of the cooling water when the motor vehicle is in standing mode. Thus, the start comfort is improved and the service life of the engine is extended.
Another contemplated arrangement for reducing the exhaust gas emission, in particular to reduce nitrogen oxides, is to meter hydrogen from the gas generating system into the exhaust gas stream.
In yet another advantageous embodiment of the present invention, in addition to the drive combustion engine, there is an electric motor which, in support of or as an alternative to the drive combustion engine, guarantees the drive of the vehicle. In case of engine damage, the APU can be switched such that, for example, it serves as the drive aggregate for the electric motor. The electric motor can be, for example, the crank or starter of the motor vehicle or a generator. Thus, the motor vehicle can be driven without external assistance to the closest repairshop. The results are advantages for off-road operation of the motor vehicle and with respect to safety in sparsely populated areas.
The additional electric motor has other advantages such as, for example, when motor vehicles are prohibited from driving due to smog. Then the motor vehicle can be operated with the combustion engine turned off, whereby the electric motor serves as the main drive of the motor vehicle. Furthermore, the electric motor can be used as the main drive, for example, in congested traffic or in city traffic (stop-and-go traffic). There are also additional advantages with respect to fuel savings.
It is also possible with the present invention to reduce a motor vehicle""s susceptibility to breakdowns with respect to the electrical supply. Thus, for example, the battery can be charged automatically by the protection circuit after prolonged periods of idling or in the case of leak current without having to start the engine and without the presence of the driver. Furthermore, the cooling water can be monitored by a sensor and, if necessary, heated so that in the winter, for example, frost damage to the cooler can be avoided.
Other advantages resulting from the integration of a hybrid system comprising a fuel cell system and battery into a motor vehicle occur at peak load on the system in the start phase, during which the use of the battery is quite conservative. In this respect one also speaks about peak shaving. Another advantage is the faster availability of larger quantities of electric energy.
In addition, the dynamics of the APU is improved during vehicle operation. The results are advantageous with respect to the service life of the APU and the drive combustion engine. To save fuel, the drive combustion engine can be turned off, for example, when driving downhill. The APU takes over the task of supplying, for example, the brake booster and the power steering with electrical power for safer driving.
In addition, the battery is discharged so as to conserve the battery when the motor vehicle is in standing mode and, at the same time, the electric consuming devices are operating, but not to the point of exhaustive discharge. Thus, it is now possible, for example, to integrate a plug with 220 V on board the motor vehicle. In addition, the energy of the battery can be used over a prolonged period of time.
To realize such a hybrid system, one can resort to the starter battery, which is already present in conventional motor vehicles. This starter battery is quite appropriate with respect to power and capacity to form together with the APU a hybrid system.
To optimize the water management of the APU, the liquid water, accumulated in the air conditioning system of the motor vehicle, can be used. This liquid water can be used, for example, to cool the fuel cell system or to moisten the gases, generated in the gas generating system. At high outside temperatures, more liquid water is accumulated owing to the operation of the air conditioning system, thus facilitating the APU management with respect to cooling capacity and water management, which is rendered more difficult during these operating conditions (high outside temperature).
Furthermore, when the engine is turned off, a larger number of electric consuming devices can be supplied with electric power than is possible in the state of the art. In addition, mechanically driven parts can be driven electrically (i.e. xe2x80x9cbeltless motorxe2x80x9d).